U.S. Published Patent Application No. 2012/0069352 describes automatic registration, which may be applied to a laser scanner. To scan a scene from different directions of view, the laser scanner is set up at different positions, from each of which one scan is generated. To register the different scans of the scene in a common coordinate system, the centers of the scans for the different laser scanner positions, which are taken by the laser scanner while scanning the scene, must be determined. Typically, targets in overlapping areas of the scans, from which the centers can be computed, are localized and identified.
Further it is known, e.g., from EP 2 322 901 A2, to use inertial measurement units in combination with GPS receivers for mobile scanning, where a pair of two-dimensional (2D) laser scanners are mounted on a car and are moved during the scan.
The type of scanner described herein is a time-of-flight (TOF) scanner that determines distance to an object based at least in part on a speed of light in air. Two common modes of operation available to a TOF scanner are a spherical mode and a helical mode. In the spherical mode, the laser scanner is fixed in position to begin a scanning procedure in which it steers a beam of light about two axes. As the beam is steered, a distance meter in the scanner measures distances and two angle measuring devices measure angles so that three-dimensional (3D) coordinates to points in the environment may be determined. In the helical mode, sometimes referred to as the mobile scanning mode, the laser scanner is moved along a path while it scans by steering a beam of light about a single axis.
In the scanning mode, it is usually necessary to move the scanner to measure multiple regions. Such regions are registered together in a single 3D scan image through the use of registration features, which may be registration targets or natural features in the environment. In most cases today, such registration is carried out in a relatively lengthy post-processing step following the collection of the scan data.
In the helical mode, the scanner is being continually moved to different regions. Such regions must likewise be tied together to provide dimensional information in all three dimensions. Because the scanner does not ordinarily directly measure movement along the direction of moving in the helical mode, some method and/or device is needed to obtain dimensional information along this direction.
Generally, there is a need today for improved methods of determining scanner movement. In the scanning mode, the movements occur between scans and, in the helical mode, the movement occur during scans.
Accordingly, while existing 3D scanners are suitable for their intended purposes, what is needed is a 3D scanner having certain features of embodiments of the present invention.